We plan to continue purification and characterization of GSH- Organic Nitrate Ester Reductase from liver and other tissues. Actually there appear to be at least two enzymes with differences in specificity toward substrates. These have been separated on DEAE-Sephadex columns. Much greater purification of the proteins with enzymatic activity in these two peaks must be achieved to determine whether there are two enzymes, more than two enzymes, multiple forms of a single enzyme, and to study the active sites and mechanisms. We plan to continue to study the selective actions of mannitol hexanitrate, erythritol tetranitrate, and glycerol trinitrate on thiol groups in the electron transport and phosphorylation enzymes of mitochondria, and on the -SH groups in soluble purified enzymes and other purified proteins.